One form of an impact printing device employs the use of a flexible endless metallic band having formed thereon a plurality of alpha-numeric characters or other forms of type characters, a plurality of timing marks and an initiating timing mark for each complete set of said characters. Typically, the type band is continuously rotated about a pair of pulleys and the type characters are moved past print positions, behind a record medium upon which printing is to be effected. Individual type hammers are usually provided for each print position or each column of the record. As any one of the type characters approaches the column in which it is to be printed, an electrical signal causes the type hammer, which is positioned opposite that column, to be moved toward the type character on the band. Said movement drives the record medium, as well as an inked ribbon, against the type font to transfer the image thereof onto the record medium.
In order to energize the proper print hammer, at the correct time, there must be some means for indicating the location of the various type characters on the type band at said proper times. Prior art printers have provided a series of timing marks on the print band and a font mark or initiating mark for each of the plurality of complete sets of characters or fonts on the band. In the prior art, the timing marks are spaced at a known distance from each other and in a known relationship to the type characters so that when the timing marks are detected, the resultant signals can be used in conjunction with certain logic circuitry to determine what character is at what position and accordingly actuate the proper print hammers.
While techniques for determining the proper position on the type font with respect to the column on the record medium and the print hammer are known, very little attention has been focused in the prior art on the need for changing the relationship between the read station and the timing marks for the purpose of shifting sideways, or laterally, the characters of a printed line. In particular, when the thickness of a record medium is changed, the amount of time required for the print hammer to impact the type font on the type band changes and accordingly the position of the printed image changes with respect to the column location on the record medium. The present system provides a means for readily effecting a lateral shift of the printed image to accommodate a change in the thickness of paper or simply to accommodate a need for a shift of the printed record which such need may arise for instance because of the position of the paper or record as it is carried on the paper tractors.